It is often useful to mount a vertical post near the edge of a concrete slab. For example, the balconies in modern apartment buildings are often formed of a concrete slab which projects from the building. To prevent people and objects from accidentally falling off such balconies, railings are provided around the balconies. Such railings are typically mounted on posts which are fastened to the concrete slab. To maximize the useful area of the balcony the balcony railing mounting posts must be attached as close as possible to the edge of the slab. Prefabricated posts may also be used to support railings on concrete stairways, railings on the sides of loading docks, and other similar fixtures to concrete structures.
Prior art prefabricated posts comprise a vertical member which forms the body of the post. The prior art offers various methods for mounting the body of the post to a concrete slab.
One method of mounting a post in a concrete slab is to drill a hole in the concrete slab large enough in diameter to accept the lower end of the body of the post. After the hole has been drilled in the concrete slab, the hole is partially filled with an expandable grout or similar material and the end of the post is placed in the hole. The grout then hardens to hold the post, in place. The lower portion of the post may have a bumpy or roughened outer surface for better retention in the hole.
A disadvantage of this mounting method is that a large hole must be drilled to mount each post. This can weaken the concrete slab, particularly if the hole is near the edge of the slab.
It is also very time consuming to drill a large hole in concrete. The time necessary to drill a hole increases very quickly as the diameter of the hole increases. Furthermore, the larger and deeper the hole the more likely it is that the drill will hit a piece of reinforcing bar in the cement slab during the drilling. If a piece of reinforcing bar is hit the hole may need to be relocated.
It must also be remembered that posts are often mounted at the edge of balconies which may be very high off the ground and are a dangerous place to work. Workers who need to drill a large number of large holes for attaching posts must spend many hours in this dangerous environment. In a residential apartment building it would not be unusual for more than one thousand posts to be installed during the construction of the building.
A second mounting means for a post provides a flat base on the lower end of the body of the post and a rigid mounting rod extending from the centre of the base. The mounting rod is grouted into place in a hole in the top surface of the slab as described above. The rod may have a bumpy or roughened outer surface for better retention in the hole. The base sits on the top surface of the slab and enhances the stability of the post.
The rod in this second variety of post may be smaller in diameter than the body of the post. The base provides some support for the post. However, the rigid mounting rod provides most of the support for the post. Because the mounting rod must be sufficiently rigid to support the post and it is not economical to make the rod from an exotic, high strength material the mounting rod is generally reasonably large in diameter.
Prior art posts of the second kind described above are typically installed near the edge of a concrete slab by drilling a hole in the top surface of the concrete slab of a size sufficient to accept the protruding rod. The balcony railing posts which are used to support balcony railings in a residential apartment building typically have mounting rods with diameters between 3/4 inch and 1 inch. It is time consuming to drill the holes necessary to mount the many posts which are required to support balcony railings in a typical apartment building.
A principal difficulty with prior art posts of either of the kinds described above is that to mount the post near the edge of a concrete slab a relatively large diameter hole must be drilled close to the edge of the slab. Because the portion of the slab between the hole and the edge of the slab is relatively thin, this portion of the slab is quite fragile. If a large force is applied to the top of the post, the rod and/or the outer portion of the bottom of the vertical member may exert enough force to crack the thin portion of the concrete which forms the outer wall of the mounting hole. Even if the concrete does not fall away completely, cracks may eventually allow water to trickle into the vicinity of the rod causing the rod to rust. The accumulation of rust in the mounting hole causes additional forces on the walls of the mounting hole which may cause the layer of cement at the edge of the slab to crack away completely.
The second variety of prior art posts described above has several disadvantages. If the top surface of the slab is not level, for example, if the top surface of the slab is slanted to shed rain, then the post cannot be easily installed so that it is vertical. The base of the post must sit flat on the top surface of the slab to provide some support to the post. Secondly, because the post relies upon the base for support, the material under the base must be strong. The top surfaces of some concrete slabs are covered with a layer of relatively soft waterproof topping material. In such cases, the second variety of post should either be installed before the topping material is applied or the topping material must be removed from the surface of the slab in the area where the base of the post will sit. This makes it expensive to install such posts. Finally, it is expensive to make the second variety of post because the base and mounting rod must be attached to the body of the post, usually by welding. This is difficult to automate on a small scale.
A third variety of prior art post has a flange around the lower end of the post body. The flange has a number of holes through it. The post is attached to a cement slab by drilling relatively small holes in the slab in a pattern corresponding to the pattern of the holes in the flange, inserting anchors in the holes, inserting screws through the holes in the flange and into the anchors and tightening the screws. The steps of installing and tightening the screws make this type of post time consuming to install.